1. Field of the Invention
This invention pertains to the field of polyurethane foams. More particularly, this invention relates to the use of a certain combination of polyols useful in preparing rigid polyurethane foams of excellent dimensional stability and heat distortion properties.
2. Description of the Prior Art
It is known to prepare foam from polyurethanes by the reaction of a polyisocyanate, a polyol and a blowing agent such as a halogenated hydrocarbon, water or both, in the presence of a catalyst. One particular area of polyurethane technology is based upon rigid polyurethane foams.
The art is replete with a wide variety of polyols useful as one of the main components in preparing polyurethanes such as polyurethane foams. As an example, U.S. Pat. No. 2,965,615 suggests use of copolymers of alkenyl-substituted aromatic compounds such as styrene, and ethylenically unsaturated monohydric alcohols such as allyl alcohol as a useful resinous polyol in urethane production. Also disclosed as useful polyol sources are alkoxylated reaction products of the above copolymers.
It has now been found that in the rigid polyurethane foam field, a special combination of polyols involving the just-mentioned allyl alcohol-styrene copolymer constituent yields a final polyurethane rigid foam of excellent dimensional stability and heat distortion properties. It has been found that use of a styrene-allyl alcohol copolymer in preparing rigid polyurethane foams leads to serious handling problems of the copolymer in that it is itself a solid. Likewise, the alkoxylated copolymer, while it can be handled in an acceptable manner, has a hydroxyl number too low to prepare suitable rigid foams.
It was therefore an object of the present invention to prepare a polyol useful in the rigid polyurethane field based on an allyl alcohol-styrene copolymer which could be conveniently handled, and yet yielded a final rigid polyurethane foam of suitable physical properties, and particularly acceptable dimensional stability and heat distortion temperature properties.